Solar cells are photovoltaic devices which convert the sun's solar energy into useful electrical energy. These solar cells may comprise a matrix or array of doped semiconductor spheres embedded in a light-reflective aluminum foil, the semiconductor material typically comprising silicon. One such solar cell is disclosed in U.S. Pat. No. 5,028,546 to Hotchkiss, entitled "Method for Manufacture of Solar Cell with Foil Contact Point", assigned to the same assignee of the present invention, the teachings of this patent incorporated herein by reference. These solar cells typically are composed of a transparent matrix provided with spheroidal particles of silicon, each particle having a p-region exposed on one matrix surface, and an n-type region extending to an opposed matrix surface. Electrical energy is produced when photons of light strike the silicon sphere, inducing electrons to cross the depletion region between the two conductivity types.
To create the n-region in the silicon sphere, the spheres are doped, typically with phosphorus. Several sources are available for doping these spheres with phosphorus, however, not all phosphorus doping sources will create an adequate phosphorus rich glass (PSG) on the silicon surface during diffusion for impurity gettering. In addition, the prior art phosphorus sources typically are restricted chemicals and require special shipping, handling, and disposal requirements. In addition, the cost of these phosphorus sources is relatively expensive.
It is desired to fabricate an n-type layer on a p-type semiconductor particle having a resistivity range which provides maximum solar conversion efficiency. The method for creating the n-type layer would preferably be derived from a dopant source that is not a restricted chemical nor poses any special shipping, handling or disposal requirements. The method should cost significantly less than other methods, and create a PSG layer on the silicon surface during diffusion.